1. Field of the Invention
This invention relates to an image pickup apparatus, such as an electronic camera, arranged to pick up an image by exposing an image sensor to an image light.
2. Description of the Related Art
During recent years, image pickup apparatuses such as an electronic camera or the like arranged to pick up an image by exposing an image sensor to an image light and display the image on a monitor, record the image on a recording medium or variously process or edit the image by taking the image into a personal computer either directly or through a recording medium, have become popular.
The image sensor employed in the electronic camera of such a kind has a narrow latitude for incident light. Therefore, the image sensor must be exposed to the image light in an accurate amount of exposure. In particular, accurate exposure control is required in a flash emission mode in which an image is to be picked up with the aid of a flash light.
Since the exposure latitude is narrow, the image pickup apparatus of this kind has generally employed, in the flash emission mode, such technique that, prior to a main exposure by which an image is actually picked up, a preliminary exposure is performed with a preliminary light emission made so as to measure an exposure condition for an object, an emission condition of a main light emission is obtained on the basis of light measurement data obtained as a result of the preliminary exposure, and the main exposure is then performed with the main light emission made under the emission condition.
In such conventional technique, the light emission time of the preliminary light emission is decided according to information on a distance to the object. In other words, the light emission time of the preliminary light emission is decided to be relatively long for an object located at a long distance and to be relatively short for an object located at a near distance.
However, according to the conventional technique, the maximum amount of emission of the main light emission naturally becomes smaller when the preliminary light emission has been made than when the preliminary light emission has not been made. Particularly, in the event of a long-distance object requiring a longer light emission time of the preliminary light emission, the charging voltage of a main capacitor remaining after the preliminary light emission decreases to a greater degree than in the event of a short-distance object. In that event, a disadvantage resulting from the decrease of energy for the main light emission becomes more serious.
Besides the decrease in charging voltage of the main capacitor caused by the preliminary light emission, the charging voltage remaining after the preliminary light emission comes to vary every time a shot is taken. Therefore, according to the conventional technique, in order to perform an accurate exposure during the main light emission, it is necessary to additionally provide some circuit for detecting the charging voltage of the main capacitor remaining after the preliminary light emission or to arrange some table or a formula relative to the remaining charging voltage. Such an arrangement is extremely disadvantageous with respect to the cost of manufacture or development of products.
This invention is directed to the solution of the problems mentioned in the foregoing. It is, therefore, an object of this invention to provide an exposure control method most apposite to an electronic camera.
It is another object of this invention to provide an image pickup apparatus having a simple exposure control arrangement for reduction in cost and also to provide an exposure control method for the image pickup apparatus.
To attain the above-stated objects, an image pickup apparatus arranged as a preferred embodiment of this invention comprises image pickup means, light emission means for illuminating an object by emitting light, light measuring means for measuring a luminance of the object on the basis of a signal from the image pickup means, distance measuring means for measuring a distance to the object, operation means for performing a first operation and a second operation for picking up an image of the object, and control means, in which, in response to the first operation of the operation means, the control means causes the light measuring means to measure the luminance, determines whether or not light emission by the light emission means is necessary according to information on the luminance measured by the light measuring means and causes the distance measuring means to measure the distance, and in response to the second operation of the operation means, if light emission by the light emission means is necessary, the control means first controls an iris on the basis of information on the distance measured by the distance measuring means, causes the light emission means to emit light for a predetermined period of time and causes a preliminary exposure to be made on the image pickup means, and then the control means causes the light emission means to emit light for a period of time decided on the basis of information on the luminance measured by the light measuring means during the preliminary exposure and causes a main exposure to be made on the image pickup means.
An image pickup apparatus arranged as another preferred embodiment of this invention comprises image pickup means, light emission means for illuminating an object by emitting light, light measuring means for measuring a luminance of the object on the basis of a signal from the image pickup means, distance measuring means for measuring a distance to the object, operation means for performing a first operation and a second operation for picking up an image of the object, and control means, in which, in response to the first operation of the operation means, the control means causes the light measuring means to measure the luminance, determines whether or not light emission by the light emission means is necessary according to information on the luminance measured by the light measuring means and causes the distance measuring means to measure the distance, and in response to the second operation of the operation means, if light emission by the light emission means is necessary, the control means first controls an iris into an aperture value having a greater amount of stopping-down selected from between an aperture value decided on the basis of information on the distance measured by the distance measuring means and an aperture value decided on the basis of a program diagram, causes the light emission means to emit light for a predetermined period of time and causes a preliminary exposure to be made on the image pickup means, and then the control means causes the light emission means to emit light for a period of time decided on the basis of information on the luminance measured by the light measuring means during the preliminary exposure and causes a main exposure to be made on the image pickup means.
The above and other objects and features of this invention will become apparent from the following detailed description of embodiments thereof taken in connection with the accompanying drawings.